Method and apparatus for conducting different investigations simultaneously in boreholes



GIFS QR' 21,351,177

H. G. DOLL 2,357,177

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AM. 75g/5? Patented Aug. 29, 1944 .toom

UNITED STATESvk PATENT OFFICE METHOD AND APPARATUS FOR CONDUCT- INGDIFFERENT INVESTIGATIONS SIMUL- TANEOUSLY IN BOREHOLES Henri GeorgesDoll, Paris, France, assignor, by

mesne assignments, to Schlumberger Well Surveying Corporation, Houston,Tex., a corporation of Delaware Application December 12, 1939, SerialNo. 308,767 In France December 16, 1938 13 Claims.

The present invention relates to the investigation of bore holes drilledinto the earth and more particularly to methods and apparatus forsimultaneously investigating a plurality of different subjects ofinterest in a bore hole.

More specifically, it relates to methods and apparatus of this characterin which the response of investigation means disposed in the bore holeis transmitted electrically to indicating means located a considerabledistance away as, for example, at the surface of the earth.

This application is concerned particularly with those subjects ofinvestigation in a bore hole which either provide information about thegeologic formations through which it extends, or which are indicative ofconditions therein, The subjects most generally investigated in a borehole include the relative impedance, apparent resistivity and thermalconductivity of the formations surrounding the bore hole, and thespontaneous potentials existing in it. Also, indications are frequentlyobtained of the temperature of the bore hole and the temperature andresistivity of any liquid contained therein.

An important object of the invention is to provide a new and improvedmethod and apparatus for simultaneously investigating a plurality ofdifferent subjects of interest in a bore hole in which the number ofconductors connecting the investigation means in the bore hole withindicating means at the surface of the earth is reduced to a minimum.

A further object of the invention is to provide a new and improvedmethod and apparatus of the above character in which the responses ofthe investigating means corresponding to the respective subjects beinginvestigated are transmitted electrically to suitable indicating meansat the surface of the earth through a single electrical circuit,comprising preferably a single conductor.

The objects of the invention are attained by employing investigatingmeans which is adapted to provide a plurality of electrical values, suchas currents or potential differences, for example, of different andseparable character, each of which is a function of a subject ofinterest in a bore hole. These electrical values of different characterare transmitted through a single circuit to the surface of the earthwhere they are indicated separately by suitable indicating means.

Where an electrical characteristic of the formations surrounding thebore hole is to be investigated at several different depths ofinvestigation, as disclosed in my copending application Serial No,190,652, led February 15, 1938, now U. S. Patent No. 2,317,259, datedApril 20, 1943, the investigating means may be adapted to set up aplurality of different electrical fields in the formations which are ofsuch character that they may be readily separated from one another. Theexpression depth of investigation as used herein and in this art meansgenerally lateral depth or horizontal distance, as referred to the Wallof the bore hole. Electrical characteristics of the created elds areobtained, which are, respectively, functions of different electricalcharacteristics of the formations. The electrical characteristics of thecreated elds are transmitted through a single electrical circuit tosuitable means at the surface of the earth for indicating themseparately.

The invention also contemplates the investiga tion of the direct currenteld produced by spontaneous potentials existing in the bore holesimultaneously with a plurality of different subjects of interesttherein, as described in detail below.

Additional features of the invention will become apparent from thefollowing detailed description of several specific embodiments taken inconnection with the accompanying drawings in which:

Figure 1 is a schematic diagram of apparatus constructed according tothe invention for simultaneously obtaining indications of an electricalcharacteristic of the formations at two different depths ofinvestigation, together with spontaneous potentials existing in the borehole;

Figure 2 illustrates schematically a modified form of indicating meansfor use in connection with the apparatus shown in Figure 1; and

Figure 3 is a schematic diagram illustrating apparatus constructedaccording to the invention for simultaneously obtaining indications ofan electrical characteristic of the formation at two different depths ofinvestigation, together with the temperature of the liquid contained inthe bore hole.

Considering Figure 1, a bore hole I0 is shown in cross-sectioncontaining the liquid II into which the investigation means I2 islowered. Ordinarily the investigating means I2 will be enclosed in asuitable casing, but for the sake of clarity, this is not shown in thedrawings.

The investigating means I2 in the bore hole includes a source of currentI3, such as for eX- ample, a battery which supplies current to a directcurrent motor I4 adapted to drive the alternators I5 and I6,respectively. The alternator I6 provides alternating current which isdifferent in frequency from the alternating current supplied by thealternator I5. For example, if the alternator I5 generates 120 cyclealternating current, the alternator I6 should be designed to generate240 cycle alternating current. A1- though any suitable frequencies maybe chosen, it is desirable for constructional reasons that the frequencyof one alternator be twice that of the other, because this may beaccomplished conveniently by providing one alternator with twice as manypoles as the other.

The alternator I5 is connected through the conductors I8 and I'Irespectively, to a pair of spaced electrodes A2 and B2 respectively,which are adapted to set up a 120 cycle alternating field in theformations surrounding the bore hole. In similar fashion, the alternatorI5 is electrically connected through the conductors I9 and 20,respectively, to a second pair of spaced `electrodes AI and BI, whichare adapted to set up a 240 cycle electric field in the formationssurrounding the bore hole.

For the purposes of this description, it will be assumed that theelectrodes BI and B2 are spaced at a considerable distance as, forexample, a few yards from the electrodes AI and A2 and that theelectrodes AI and A2 are spaced from each other a muchv shorterdistance, such as for example, a few feet. It is to be clearlyunderstood, however, that these distances are given merely by way ofexample and any other electrode spacings may be used, depending on theresults desired.

Located in the vicinity of the electrodes AI and A2 is a potentialelectrode M which is connected to a single conductor 2I upon which theinvestigating means I2 is supported in the bore hole I0, and throughwhich its respective responses are transmitted electrically toindicating means at the surface of the earth. For convenience, it willbe assumed that the distance between the electrode AI and the electrodeM is in the neighborhood of the diameter of the bore hole, and thedistance between the electrode M and the electrode A2 is several timesthe diameter of the borehole. For the sake of clarity, the respectivedistances between the electrodes `have not been 4shown in the drawingsin their proper relationship to the diameter of the bore hole.

The indicating means at the surface of the earth includes a circuit 22for obtaining indications ofcontinuous potentials, a circuit 23 forobtaining indications of 120 cycle alternating current potentials and athird circuit 24 for obtaining indications of 240` cycle alternatingcurrent potentials. The indicating circuits 22, 23 and 24 are connectedin parallel, one end 25 of the parallel circuit being connected to theconductor 2|, and the other end 26 being connected through a conductor21 to a ground point N at the surface of the earth.

The circuit 22 for providing indications of continuous potentialsincludes a recording type continuous potential indicating instrument GIconnected in series with a lter FI which is designed to prevent theilowfof any alternating current therethrough,

The circuit 23 for obtaining indications of 120 cycle alternatingcurrent potentials includes a recording type alternating currentindicating instrument G2 connected in series with a condenser Cz forblocking the passage of continuouscurrents, and a filter F2 of the bandpass type adapted to pass alternating current in the frequency range ofto 150 cycles, for example.

'I'he circuit 24 for obtaining indications of 240 cycle alternatingcurrent potential differences includes a recording type instrument G3for providing indications of alternating current potential diierences,connected in series with a condenser C3 for blocking the passage ofcontinuous currents and a filter F3, which may also be of the band passtype, designed to pass alternating currents in the frequency range from210 to 260 cycles, for example.

In operation, the alternator I5 supplies 120 cycle alternating currentto the electrodes A2 and B2 creating a 120 cycle alternating field inthe formations surrounding the bore hole. This alternating field in theformations produces a corresponding alternating potential differencebetween the electrode M in the bore hole and the electrode N grounded atthe surface of the earth, which is a function of the impedance orapparent resistivity of the formations. This potential difference istransmitted through the conductor 2I, the condenser C2, and the filterF2 to the alternating current indicating instrument G2, thus providingindications of the impedance or apparent resistivity of the formationsat one depth of investigation.

At the same time, the 240 cycle potential difference impressed upon theelectrodes AI and BI by the alternator I6 creates a corresponding 240cycle alternating field in the formations, thereby producing a 240 cyclealternating potential diiference between the electrode M in the borehole and the electrode N, which is a function of the impedence orapparent resistivity of the formations at a different depth ofinvestigation. This 240 cycle potential difference is transmittedthrough the conductor 2I, the condenser C3 and the filter F3 to thealternating current indicating instrument G3, thereby providingindications of apparent resistivity at a second depth of investigation.

Meanwhile, the direct current eld produced by spontaneous potentialsexisting in the bore hole creates a continuous potential differencebetween theelectrodes M and N which is transmitted through the conductor2l and the filter FI to the continuous potential indicating instrumentGI, thereby providing indications of spontaneous potentials in the borehole.

As disclosed in my above mentioned copending application, by comparingthe indications of irnpedance or apparent resistivity obtained at twodifferent depths of investigation, highly accurate data regarding thetrue resistivity of the strata may be obtained in bore holes in whichportions of the strata are flooded with bore hole liquid.

If desired, vibration type galvanometers may be used, as shown in Figure2, for recording directly and separately current amplitudescorresponding to the respective frequencies, instead of the ltercircuits illustrated in Figure 1. Where thisis done, one of thealternating current indicating circuits may be dispensed with and asingle circuit 21 may be utilized to provide indications of both thecycle and the 240 cycle alternating potential differences between theelectrode M in the bore hole and the electrode N grounded at the surfaceof the earth.

The indicating circuit 21 includes a vibration type galvanometer GZ,resonant at 120 cycles, and a vibration type galvanometer G3 resonant at240 cycles, connected in series with acondenser CI, the function ofwhich is to prevent direct current from passing to galvanometers Gf 2and G'3. The galvanometers G| and G2 and G3 may be of the recordingtype, in Which case a record may be obtained of the direct currentpotential, the 120 cycle alternating potential and the 240 cyclealternating potential between the electrode M in the bore hole and theelectrode N at the surface of the earth.

If desired, another subject of interest, such as for example thetemperature of the liquid in the bore hole may be investigated, togetherwith the impedance or apparent resistivity of the formations at twodifferent depths in the bore hole, and the spontaneous potentialsexisting therein, as shown in Figure 3.

This modification is similar to the apparatus illustrated in Figure 1,except that it includes a third alternator 2B which is also adapted tobe driven by the direct current motor |4, and which is connected throughthe conductors 29 and 30, respectively, to the apices 3| and 32 of aresistance bridge responsive to variations in temperature. Theresistance bridge may be of the type described in my copendingapplication Serial No. 181,879, filed December 27, 193'1, now U. S.Patent No. 2,249,751, dated July 22, 1941, and it may comprise, forexample, a pair of resistors 33 and 34 having a relatively hightemperature coefficient of resistivity, connected to a second pair ofresistors 35 and 36 having a negligible temperature coefficient ofresistivity.

The alternator 28 should be designed to supply alternating current whichis different in fre- `quency from the frequencies of the current sup- Iplied by the alternators l and I6 and its frequency may be, for example,360 cycles.

Alternating current of this frequency is supplied through the conductors29 and 3l) to the apices 3| and 32 of the resistance bridge. The valuesof the resistors 33, 34, and 36 are so chosen that for a given referencetemperature the bridge is in equilibrium and no potential dif` ferenceexists across the apices 31 and 38. In this modification, the potentialelectrode M in the bore hole is connected through a conductor 39 to theapex 38 of the resistance bridge, the other apex 31 of which isconnected to the conductor 2|.

The indicating apparatus at the surface of the earth is analogous to theindicating apparatus disclosed in Figure 1, except that it includes anadditional indicating circuit 40 for providing indications of 360 cyclealternating potential differences between the electrode M in the borehole and the electrode N grounded at the surface of the earth. Thecircuit 4|] includes a recording type instrument G4 for providingindications of alternating potentials, which is connected in series witha condenser C4, for blocking the passage of direct current, and a lterF4. The filter F4 may be of the band pass type, designed to permit` Ifthe temperature of the bore hole liquid is .ril

different from this equilibrium temperature,'then a 360 cyclealternating potential difference will exist across the apices 31 and 38of the resistance bridge, which will be transmitted through theconductor 2|, the condenser C4, and the filter F4 to thealternatingcurrent potential indicating instrument G4, thereby providingindications of the difference in temperature.

While alternating currents of any desired frequency may be employed, thefrequencies chosen should preferably be substantially different from thefrequencies of the currents supplied by power companies in the region ofthe bore hole. Where this is done, parasitic potential differences whichmight be produced by leakage through the ground or by induction in themeasurement circuit are eliminated. Inasmuch as frequencies of or 60cycles are often used in bore hole regions, frequencies -substantiallyhigher than these have been chosen in the above description. It shouldbe understood, however, that frequencies lower than 50 or 60 cycles maybe used with good results.

It will be apparent from the foregoing, that instead of obtainingindications of resistivity at two different depths of investigation,indications of resistivity might be obtained at three or four differentdepth-s of investigation, if desired- This may be accomplished byproviding the appropriate number of energizing circuits in the borehole, together with corresponding indicating circuits at the surface ofthe earth.

While several specific embodiments have been described in the foregoingspecification, the invention is not intended to be in any way limitedthereby, but is susceptible of numerous changes in form and detailwithin the scope of the appended claims.

Iclaim:

1. A method of obtaining indications simultaneously of two differentelectrical characteristics of the formations surrounding a bore hole andspontaneous potentials existing therein, comprising the steps ofsimultaneously creating two separably different electric fields in theformations, obtaining electrical values from said respective fieldswhich are functions of the respective electrical characteristics of theformations to be investigated, obtaining continuous potentials which area function of spontaneous potentials existing in the bore hole,combining said electrical values and continuous potentials, transmittingsaid combined electrical values and potentials to the surface of theearth, and obtaining separate indications of said respective electricalvalues and continuous potentials.

2. A method of obtaining indications simultaneously of two differentelectrical characteristics of the formations surrounding a bore hole andof spontaneous potentials existing therein, comprising the steps ofsimultaneously creating two alternating electrical fields of differentfrequency in the formations, obtaining alternating potential diiferencesbetween two points in said fields and produced thereby, each of whichpotential differences is a function of an electrical characteristic ofthe formations, obtainingvcontinuous potentials produced by spontaneouspotentials in the bore hole, combining said alternating potentialdifferences and continuous potentials, transmitting said combinedalternating potential differences and continuous potentials to thesurface of the earth, separating said respective alternating potentialdiiTerences and continuous potentials, and obtaining indications of saidseparated alternating potential differences and continuous potentials.

3. Apparatus for determining the nature of earth formations traversed bya bore hole having a continuous electric field therein which is afunction of spontaneous potentials existing therein, comprising meansfor simultaneously creating a plurality of alternating electric fieldsof different frequency in the formations, a grounded conductor connectedto an electrode disposed in the bore hole in the vicinity of saidcreated elds, for transmitting electrical characteristics of saidcreated fields and any continuous electric field to the surface of theearth, means for separating said respective characteristics, and meansfor providing indications of said separated characteristics.

4. Apparatus for investigating a plurality of different subjects ofinterest in a bore hole, comprising means for simultaneously creating aplurality of separably different electric fields in the formationssurrounding the bore hole, electrical indicating means, an electricalcircuit for transmitting to said indicating means electricalcharacteristics of said created fields, which are respectively functionsof different electrical characteristics of the formations, and means forsimultaneously producing in said electrical circuit a voltage which is afunction of at lea-st one other subject of investigation in the borehole.

5. Apparatus for investigating a plurality of different subjects ofinterest in a bore hole having an electric field therein which is afunction of spontaneous potentials existing therein, comprising meansfor simultaneously creating a plurality of different periodicallyvariable electric fields in the formations, indicating mean-s, anelectrical circuit for transmitting to said indicating means anelectrical characteristic of said continuous field which is a functionof spontaneous potentials existing in the bore hole, and electricalcharacteristics of said periodically variable elds which arerespectively functions of different electrical characteristics of theformations, and means for simultaneously producing in said electricalcircuit a voltage which is a function of at least one other subject ofinvestigation in the bore hole.

6. Apparatus for investigating a plurality of different subjects ofinterest in a bore hole, comprising means for simultaneously creating aplurality of separably different electrical fields in the formationssurrounding the bore hole, a grounded conductor connected to anelectrode disposed in the bore hole in the vicinity of said createdfields, for transmitting to the surface of the earth electricalcharacteristics of said different created iields which are respectivelyfunctions of different electrical characteristics of the formation-s,means for simultaneously producing in said conductor a voltage which isa function of at least one other subject of investigation in the borehole, means for separating said voltage and respective electricalcharacteristics in the conductor from each other, and means forproviding indications of said separated voltage and electricalcharacteristics.

7. Apparatus for investigating a plurality of different subjects ofinterest in a bore hole having a continuous electric field therein whichis a function of spontaneous potentials existing therein, comprisingmeans for simultaneously creating a plurality of alternating electricfields of different frequency in the formations surrounding the borehole, a grounded conductor connected to an electrode disposed in thebore hole in the vicinity of said created fields, for transmitting tothe surface of the earth electrical characteristics of said differentcreated fields which are respectively functions of different electricalcharacteristics of the formations, and an electrical characteristic ofsaid continuous field which is a function of spontaneous potentials inthe bore hole, means for simultaneously producing in said conductor avoltage which is a function of at least one other subject ofinvestigation in the bore hole, means for separating said voltage andrespective electrical characteristics in the conductor from each other,and means for providing indications of said separated voltage andelectrical characteristics.

8. Apparatus for investigating bore holes, comprising a plurality ofspaced current electrodes adapted to be lowered into the bore hole, analternator connected to two of said current electrodes for creating analternating current field of first frequency in the formations, a secondalternator connected to two different current electrodes for creating analternating current field of second frequency in the formations, a motorfor driving said alternators, a source of voltage for said motor, aconductor having its upper end grounded at the surface of the earth andbeing -connected to an electrode disposed in the bore hole in thevicinity of said created fields, alternating current indicating meansconnected to said conductor, lter means for blocking the passage ofalternating current of second frequency to said indicating means, secondalternating current indicating means connected to said conductor, secondfilter means for blocking the passage of alternating current of firstfrequency to said second indicating means, continuous current indicatingmeans connected to said conductor, and third filter means for blockingthe passage of alternating currents to said last-named indicating means.

9. Apparatus for investigating bore holes, comprising a plurality ofspaced current electrodes adapted to be lowered into the bore hole, analternator connected to two of said current electrodes for creating analternating current field of first frequency in the formations, a secondalternator connected to two different current electrodes for creating analternating current field of second frequency in the formations, a motorfor driving said alternators, a source of voltage for said motor, aconductor having its upper end grounded and being connected to anelectrode disposed in the bore hole in the vicinity of said createdelds, indicating means resonant at said first frequency connected tosaid conductor, second indicating means resonant at said secondfrequency connected to said conductor, continuous current indicatingmeans connected to said con-` ductor, and filter means for blocking thepassage of alternating current to said last-named indicating means.

l0. Apparatus for investigating bore holes, comprising a plurality ofspaced current electrodes adapted to be lowered into the bore hole, analternator connected to two of said current elec-v trodes for creatingan alternating current field of first frequency in the formations, asecond alternator connected to two different current electrodes forcreating an alternating current field of second frequency in theformations, an impedance bridge responsive to variations in temperaturein the bore hole, a third alternator connected across one diagonal ofsaid bridge for supplying alternating current of third frequencythereto, a motor for driving said alternators, a source of voltage forsaid motor, a conductor having its upper end grounded, said conductorbeing connected in series with the other diagonal of the bridge and toan electrode disposed in the bore hole in the vicinity of said createdfields, a plurality of alternating current indicating means connected tothe conductor, said indicating means being responsive only toalternating currents of said rst, secnd and third frequencies,respectively, and continuous current indicating means connected to saidconductor.

11. A method of simultaneously investigating electrical characteristicsat different depths of investigation of the formations surrounding abore hole, comprising the steps of simultaneously generating in the borehole a plurality of alternating currents of different frequencies,passing all of said generated currents through the adjoining formationsby applying them to the formations in such a way as to be differentlyaffected by electrical -characteristics of the formations at differentdepths of investigation, obtaining electrical values from saidrespective currents resulting from their passage through saidformations, which values are functions of the electrical characteristicsof the formations at different depths of investigation, respectively,combining said electrical values, applying said combined electricalvalues to a single electrical circuit, and obtaining therefrom at thesurface of the earth, separate simultaneous indications of saidelectrical values.

12. A method of simultaneously investigating electrical characteristicsat different depths of investigation of the formations surrounding abore hole, comprising the steps of simultaneously Y generating in thebore hole a plurality of alternating currents of different frequencies,passing .all

of said generated curents through the adjoining formations by applyingthem to the formations in such a way as to be differently affected byelectrical characteristics of the formations at different depths ofinvestigation, obtaining alternating potential differences from saidrespective currents resulting from their passage through saidformations, which alternating potential differences are functions of theelectrical characteristics of the formations at different depths ofinvestigation, respectively, combining said alternating potentialdifferences, applying said combined alternating potential differences toa single electrical circuit, and obtaining therefrom at the surface ofthe earth separate simultaneous indications of said alternatingpotential differences.

13. Apparatus for simultaneously investigating electricalcharacteristics at different depths of investigation of the formationssurrounding a bore hole, comprising means to generate simultaneously inthe bore hole a plurality of alternating currents of differentfrequencies, means to pass all of said generated currents through theadjoining formations in such a way as to be differently affected byelectrical characteristics of the formations at different depths ofinvestigation, means in the bore hole to pick up electrical values fromsaid respective currents resulting from their passage through saidformations, a lsingle electrical circuit extending to the surface of theearth, said pickup means being in electrical connection with said singleelectrical circuit to apply said electrical values to said singleelectrical circuit, means at the surface of the earth for simultaneouslyseparating said electrical values from each other,

` and means for simultaneously indicating said separated values.

HENRI GEORGES DOLL,

